Apparatus for surveying bore holes



oef. 2s, 195s C. L. NORDEN APPARATUS FOR SURVEYING BORE HOLES FiledMarch 6, '1953 4 Sheets-Sheet 1 INVENTOR.

vCAI/ez. A/o/PDEA/ BY Afp-`L-Smm Oct. 28, 1958 c. L. NORDEN 2,857,677

APPARATUS FOR SURVEYING BORE HOLES Filed March 6, l955 4 Sheets-Sheet 2IN V EN TOR.

12.1.5 E Cnel. A/QQDEA/ BY Mm@ 7'7 ORME Y Oct. 28, 1958 C. L. NORDENAPPARATUS FOR SURVEYING BORE HOLES Filed March 6, 1953 4 Sheets-Sheet 344 Il, 5o I 46 sa o 48 4o ,n I

|| f H n l u 58 62' Zo v INVENToR. @22A L A/oQoE/V HTTOP/VEY Oct. 28,1958 c. L. NoRDl-:N '2,857,677

APPARATUS FOR SURVEYING BORE HOLES Filed March 6, 1953 4 Sheets-Sheet 4INDlATED REFERENCE.

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TQQE QEr-Er-zENea 'DlQEC-TION PLANE NORMAL TO AXIS OF BOQE HOLEINVENTOR. C nel. L. A/o/@DEA/ BY MLM 4 TTOENE Y PLANE oF Hok/zou thesurface of the earth.

United States Patent 1 APPARATUS FOR SURVEYIN G BORE HOLES ApplicationMarch 6, 1953, Serial No. 340,799

8 Claims. (Cl. 315-2055) My invention relates to apparatus for surveyingbore holes and more particularly to a device for measuring theinclination of bore holes from the vertical and the direction of theinclination in azimuth with reference to a selected direction. i

This application is a continuation in part of my copending applicationSerial No. 2,975,'led January 19, 1948, for Apparatus for Surveying BoreHoles, now Patent No. 2,699,611 issued Ianuary18, 1955.

In the drilling of oil wells, the drill bit must pass through variousgeological strata having different characteristics. These differentcharacteristics cause the drill bit to deviate from the vertical, and awhipstock is employed to bring the bit back to vertical. However, theresultant bore hole will not be truly vertical. Occasionally a suitabledrilling location will not be found directly over the deposit of oil anddrilling must be done from a site at some distance from the point overthe deposit. In such a case, the bore hole must be drilled at apredetermined inclination and direction from the chosen site in order toreach the deposit. The provision of apparatus for surveying such boreholes to produce a record of the inclination of the hole at variouspoints and the direction of this inclination is exceedingly dilcult.This is especially true of many wells being drilled today, since thedeposit is often located many thousands of feet below In addition, sucha surveying instrument must occupy a space of limited cross-sectionalarea in order that it may iit within the bore hole.

Measurements of the inclination of the hole present no great problem,since any number of levels or pendulums may be used to indicate ltheamount of the inclination. Measurements of the direction of theinclination, however, present a more serious problem. Magnetic compasseshave been unsatisfactory for indicating such direction, since themagnetic characteristics of the strata through which the instrument ispassing are random and vary with time and are, therefore, exceedinglydifficult to determine. Very often the bore hole itself is provided witha casing which acts as a shield for the magnetic compass, furthercomplicating the problem.

It has been suggested that a gyrocompass be used to provide a referencedirection from which the direction of the inclination can be measured.However, errors will be introduced in the case of the gyrocompass byprecessions caused by friction in the bearings of the gyro scope 'rotorand by the rotation of the earth. No suitable means is provided in theprior art for compensating for these errors. In addition, in instrumentsof the prior art employing -gyrocompasses, electrical leads from theinin the gyroscope rotor bearings and the rotation of the earth.

In my copending application Serial No. 2,975, previously referred to, Ihave disclosed apparatus for surveying bore holes in which the spin axisis maintained in a plane normal to true gravity so that the gyroscopeernployed therein gives true directions with reference to the plane ofthe horizon. The azimuth scale, however, on which the directions areindicated, is iixed in a plane which is perpendicular to the axis of theinstrument and, therefore, to the axis of the bore h ole." Sincek theindicated directions are given in this plane, they must kbe referred tothe plane of the horizon to obtain the true directions, and it isnecessary to calculate the true direction for each reading or,observationv of indicated direction. l have also developed apparatusfor surveying bore holes which is provided with means for maintainingthe spin axis of the gyroscope ina plane which is perpendicular to theaxis of the instrument and, therefore, perpendicular to the axis of thebore hole. It is this latter apparatus which is the subject matter oflmy invention. When the spin axis of the 'gyroscope is maintained inaplane perpendicular to the axis of the bore hole, the gyroscope Willgive true directions with reference to that plane. Since the azimuthcircle is fixed in a plane perpendicular to the instrument and bore holeaxes, the gyroscope will give true directions in the plane ot theazimuth. Most bore holes have inclinations which'l are in a singlevertical plane, and the'indicated directions will be true directions. Itis therefore not necessary to correct the indicated directions as mustbe `done in the case where the spin axis is maintained in a plane normalto true gravity. Some bore holes are helical in shape and introduce agyratory motion of the instrument around a vertical axis.

Since the Cardan ring is insensitive to rotation about anyv axis atright angles to the Cardan, an error will be introduced by the gyratorymotion and a correction must be made, as will be described in detailhereinafter. However, as is pointed out above, most bore holes have alltheir inclinations in asingle vertical plane and no cor-v rections needbe made. The gyroscope of my improved apparatus -is automaticallycorrected for errors introduced by friction in the rotor bearings and bythe rotation of the earth on its axis.

One object of my invention is to provide an apparatus for surveying boreholes which eliminates the disadvantages of the prior art. i

Another object of my invention is to provide an irnproved apparatus forsurveying bore holes to determine the amount of inclination of the holeand the direction of the inclination with reference to a predetermineddirection.

Another object of my invention is the provision of apparatus forsurveyingv bore holes in which a reference direction is accurately andconstantly maintained.

AV further object of my invention is to provide an apparatus forsurveying bore holes in which a record of the anglel of inclination ofthe hole frornthe vertical and the direction of the inclination .withrespect to a predetermined direction is made.

A still further object of my invention is to provide apparatusV forsurveying bore holes having inclinations generally in a single verticalplane, which apparatus gives a record of inclinations and the directionsof the inclinations which requires no correction.

Other and further objects of my invention will appear from the followingdescription.

In generalmy invention contemplates the provision of a liquid-tightcasing having an outside diameter such that it may readily be loweredinto a bore hole. A number of housings are mounted within the casing.Disposed respectively within the various housings are a camera Patentedoct. .28, 1958 `of the bore `hole at the position of the instrument. I

accomplish this by applying correctional precessions from the servomotorand a switch. Means are provided `for correcting the servomotor forerrors in azimuth intro- -duced by precessions caused by the rotation ofthe earth onitsaxis and friction in the gyroscope rotor bearings. In theaccompanying drawings which form part of the instant `specification andwhich are to be read in conjunction therewith and in which likereference numerals are used to indicate like parts in the various views:

Figure lis a elevation of a unit embodying my apparatus `forsurveyingbore holes with a part broken away.

Figure 2 is a sectional View on an enlarged scale with part of the caseremoved taken generally on the line 2 2 of Figure 1.

Figure 3 is a sectional view taken along the line 3--3 of Figure 2.

Figure 4 is an elevation taken on the line 4-4 of Figure 2 with thecasing and housing removed.

Figure 5 is a sectional view taken along the line 5-5 of Figure 4.

Figure 6 is a sectional view taken along the line 6-6 of Figure 3.

Figure 7 is a diagrammatical view showing the electricalcircuits-employed in my apparatus.

Figure 8 is a diagrammatic elevation showing the generation ofcorrections when the spin axis of the gyroscope is maintained normal tothe axis of the bore hole.

Figure 9 is a plane view of the diagram shown in Figure 8.

More particularly, referring now to the drawings, I providealiquid-tight casing 12 having removable top and bottom members 14 and16, respectively. Casing 12 has an outside diameter such that it may belowered in a bore hole. For example, the outside diameter of casing 12may be three and one-half inches and the wall thickness SAG of an inch.Appropriate means such as an eye 18 is fixed to the top member 14 bysuitable means such as straps to provide means for-lowering theapparatus into the bore hole. The interior of casing 12 contains anumber of housings 22, 24, 26, 28 and 30, in which housings a battery, aservomotor and shockabsorbing means, a gyroscope unit, a scale unit anda camera unit are respectively disposed. The housings are separated fromone another by partitions 32. Referring to Figures 3 and 6, the rotor 34of my gyroscope is selected to have as large a moment of inertia as ispossible within limits imposed by the available space and, therefore, ismade of some heavy metal such as tungsten which is placed on a plate 36carried by the shaft 38 of the unit. Shaft 38 is supported by a pair ofball bearings 40 and 42 mounted in the gyroscope housing 44. Tubularmember 46 is'xed to the housing by suitable means such as bolts 48 and`has .pole pieces `50 and 52 formed thereon which carry respectivewindings 54 and 56. Current is supplied to the gyroscope armaturewinding 58 through brushes 60 and 62.

As is shown in Figure 6, the gyroscope housing 44 is supported on a'pairof ball bearings 64and 66 mounted on stub shafts 68 and 70,respectively, fixed to the Cardan ring 72 of the `gyroscope byappropriate means such as bolts 74. It is to be noted that stub shafts68 and 70 are aligned at right angles to the shaft 38. The Cardan ring72 is mounted for rotation about a normally vertical axis in an upperball bearing 76 and a lower ball bearing 78, as can readily be seen byreference to Figures 2 and 3. For purposes of convenience the axis CTIof shaft 38 about which the rotor y34 ofthe 'gyroscope rotates isreferred to as the spin axis. The axis which passes through stub shafts68 and 70 around which the gyroscope housing 44 pivots is referred to asthe tilt axis. The vertical axis around which the Cardan ring 72 ispivoted is referred to as the azimuth axis.

The lower bearing 78 in which the Cardan ring is carried is supported bya boss on the bottom member 80 of the housing 26. The member 80 isformed 'with a bracket 82 to which the housing 86 of a servomotor isattached. The motor shaft 84 is attached to a stub shaft 8S on thebottom 4of the Cardan ring by means of a universal joint 90. Shaft 88 isformed a't its upper end with a flange or plate 92 secured to the bottomof Cardan ring 72 by suitable means so that when shaft 84 rotates, itwill rotate shaft 38 and thereby the Cardan ring. Shaft 88 is hollow andcarries an insulating bushing 94 and supports a plurality of slip rings96 through which electrical connections to the gyroscope are made. The-base 98 of housing 24 has an upstanding annular boss 100 formed thereonwhich guides a spring 102 seated on base 98 -and extending upwardlytothe underside of base 80. A boss 104 formed on the underside of base80 holds the spring in position. The lower portion of the servomotorhousing `86 carries a guide member 106 which is slidably received in anopening formed in a bracket 108 attached to base 98 by a screw 110.Spring 102 provides means to absorb any shocks encountered when theassembly is lowered into the bore hole. When a shock is encountered, thekinetic energy of the unit enclosed in housing -26 compresses spring 102which absorbs the shock, and guide member 106 may slide downwardly inthe recess in bracket 108. The openings 112 in base 98 and 114 in theseparator 32 covering the housing 22 permitfmovementof guide member 106downwardly through the opening in bracket 108.

The upper portion of Cardan ring 72 is secured to a flange 116 formed ona shaft 1-18 rotatably mounted in bearing 76. A disk 120 of lightaluminum is carried on a pin 122 at the upper end of shaft 118 and isclamped to the shaft by a clamping nut 124. A cylindrical member 126 atthe periphery of the disk 120 has an upper flange 128 which may becalibrated in azimuth in any appropriate manner. K The Cardan ring 72 isformed with a depending portion 130 to which is secured by means ofmachine-screws 132 a plate i134. A bracket 136 on the bottom of Cardanring 72 has a recess therein in which is carried a stub shaft 138. Stubshaft 138 is securely held in bracket 136 by a screw 140. A bracket 142is adjustably fixed on shaft 138 by a set screw 144. Carried by thebracket 142 and insulated therefrom by an insulating member 146 are apair of conducting segments 148 and 150. The segments 14S and 150 areseparated by a portion 147 of the insulating member 146 extendingbetween them as can be seen by reference to Figure 4. The end of thestub shaft 138 carries a ball bearing 149 in which bearing and anotherball bearing 151 carried by `plate 134, I pivot a shaft 152. A lever 154is secured to shaft 152 for rotation therewith. A conducting arm 156 isxed to the lever 154 by a screw 158 and insulated therefrom by aninsulator 160. If desired, the lever 156 may itself be made ofinsulating material.

As can readily be seen by reference to Figures 4 and 6, an angle plate162 is secured to the `housing 44 Yof the gyroscope by a machine screw164. A connecting rod 166 is pivoted on a pin 168 on plate 162 and heldin the connected position by a spring attached to housing 44 by `a screw172. The lower end of connecting vrod 166 is pivoted around a pin 174yon lever 154- and the connection maintained by a spring 176 fixed tothe lever 154 by a screw 178. It is -to bc noted that the distancebetween the axis of shaft 70 and the axis of `pin 168 is exactly thesame as `the distance between the axis of bearing 151 and the axis ofpin center.

174. Similarly, the length of the connecting rod 166 between the axis ofpin 168 and the axis of pin 174 is thev same as the distance between theaxis of bearing 66 and the axis of bearing 151. Thereby, I have provideda parallel motion connection so that the lever 154 will always beparallel to the axis of spin of the gyroscope. Relative movement betweenthe spin axis and the direction of the bore hole as represented by theportion 147 of the insulating member 14 extending between segments 148and 150 will cause relative movement of contact arm 156 with respect tothe conducting segments. In the normal position of operation when thespin axis is exactly perpendicular to the axis of the bore hole, the endof contact arm 156 will rest on the insulation 147 between the segments148 and 150.

The upper portion of the scale unit housing 28 is closed by an annularmember 180 iixed to the housing 28 by suitable means such as screws 182and provided with a depending ange 184 forming an opening 186. The lowerend of flange 184 as viewed in Figure 3 has a peripheral lip 188 onwhich is supported a heavy glass plate 190 having a ball bearing 192seated in its This ball bearing casts a shadow at the base of the scalecompartment and, accordingly, I place all indicators, scales and thewatch out of the shadow zone. A shaft 194 carries a spherical bearingmember 196 which rests upon the balls of bearing 192. A shaft 198 issupported from shaft 194 by suitable means such as lpins 200 and carriesa base 202 for the support of the indicators at its lower end. Base 188is screwed onto threads 204 on the end of shaft 198. A thermometer (notshown) is mounted on base 202. Shaft 198 is formed with a laterallyextending bearing 206 in which is supported'a shaft 208. A pendulum 210is mounted on shaft 208 for rotation therewith and cooperates with ascale 212 calibrated to show inclinations up to 40 degrees. Likewise,secured to the base 202 in any suitable manner is an indicator 214calibrated in inclinations up to 20 degrees. I also mount a ballindicator 216 on the base 202 which has a ball 218 retained on aspherical lapped surface 220 by means of a curved glass cover 222. Thecurvature of the ball support 220 is such that it is adapted to indicateinclinations up to the vicinity of 71/2 degrees. The glass cover is alsoprovided wtih a plurality of circular etched lines to indicate 1 degreeof inclination in any direction. In addition to the indicators alreadydescribed, I provide a watch 215 on base 202. The details of theindicating means just i described are shown 'and described in detail inthe aforesaid copending application, Serial No. 2,975.

A U-shaped guide member 224 is secured to the underside of base 202 andsurrounds clamping nut 124 which is formed with a cylindrical exteriorsurface. A roller 228 is mounted for rotation about a shaft 230 carriedby the base 202. The roller 228 is adapted to contact the surface of nut124. The interior sides of the guide member 224 are likewise adapted tocontact the cylindrical nut 124. When the instrument is vertical, theassembly of scales suspended from the bearing 192 is such that theroller 228 and the interior sides of guide 224 just clear the lateralsides of nut 124. The base 202 is formed with a thickened portion 232which gives olset weight to the base on aline drawn through the axis of-roller 228 and the axis of cylindrical nut 124. This arrangementprovides friction damping permitting the base and scale assembly tostabilize at a low gravity position without undue oscillation. As theinstrument is inclined, weight 252 will cause the base to rotate to aposition where weight 232 is in the low gravity position. The lower theinclination, the greater will be the friction damping of guide plate 224against the nut 124.

The annular cover member 180 of housing 28 supports a pair of bases 234and 236 in which are mounted, respectively, incandescent lamps 238 and240. Above the scale unit in the housing 30 I mount the camera unit 6242, the lens 244 of which is shown. This cameraunit may be of anyappropriate design and is well known in the art.

Referring now to Figures 2 and 6, I mount a pair of guide members 246and 248 on the gyroscope housing 44. Guide member 246 extends verticallyof the housing in a direction parallel to the azimuth axis, as can beseen by reference to Figure 2. The guide member 248 extends horizontallyin a direction parallel to the spin axis of the gyroscope, as can beseen by reference to Figure 6. An internally threaded weight 250 ismounted on a screw 252 mounted within suitable bearings in guide member246. The shape of the weight 250 is such that it engages a portion ofthe guide member and is prevented from rotating relatively thereto. Anadjusting head 254 is provided so that on rotation thereof, weight 250will be moved up or downwardlyl along the length of screw 252. Byrotating nut 254 I can thereby raise or lower the center of gravity ofthe gyroscope housing and assembly to a point where it will coincidewith the horizontal plane passing through the tilt axis.

A second internally threaded weight 256 is mounted on a screw 258carried in suitable vbearings in guide member 248. This weight is alsoso shaped as to cooperate` with the guide 248 so that it cannot rotaterelative thereto. By means of an adjusting head 260, weight 256 can bemoved back and forth along the lengthof screw 258. The screw carries ascale which is calibrated as a function of the 'cosine of latitude, andthe weight is constructed such that it produces a moment about the tiltaxis which is a function of the distance of the center of gravity of theweight from the tilt axis and of the magnitude of the weight. Theresultant` torque will cause the gyroscope to precess in azimuth and isadapted to introduce a correction for the error introduced by precessiondue to the rotation of the earth.

The electrical connections of my assemblyare made -through the gyroscopehousing and `are diagrammatically illustrated in Figure 7. A battery 262has one of its terminals grounded at a point indicated by the referencecharacter 264 and its other'terminal connected to a conductor 266 commonto all circuits. A conductor 268 connects the contact arm 156 to theconductor 266. Conducting segment 148 on the bracket 142 is connected toone of the windings 270 of the gyroscope servomotor by la conductor 272and the other conducting segment on bracket 142 is similarly connectedto the other winding 274 of the servomotor by a lead 276. Both of thewindings 270 and 274 are connected to a brush 276 of the servomotor, andthe other servomotor brush 278 is grounded. It is to be noted thatwindings 270 and 274 connected respectively to conducting segments 148and 150 are oppositely wound with the result that the current throughone will befopposite to the current flowing through the other in theevent that its respective conducting segment is contacted by contactingarm 156. As a result, the servomotor armature will rotate in onedirection or the other depending upon which of the conducting segmentsis contacted by arm 156. A conductor 280 connects lead 266 with one ofthe brushes 60 of the gyroscope motor and also with winding 284 -of thegyroscope motor. Brush 62 of the gyroscope motor and the other end ofwinding 284 are grounded. A lead 288 connects conductor 266 with a brush290 and the winding 292 of thecamera motor. Brush 294 and rthe other endof the winding 292 of the camera motor are grounded. Incandescent lamps238 and 240 are likewise connected between conductor 266 and ground.

In use, the camera unit of the apparatus is loaded v with lm and 'theswitch to the current supply of the p camera and incandescent lampsisclosed. The scale on and the azimuth scale has been oriented to thedesired direction, the units areassembled -as shown in Figure 'l and alowering cable attached tothe eye 18. The-instrument is then loweredinto the bore hole and its position in depth ascertained by a suitablecalibrated lowering reel or by appropriate markings onthe lowering cableor both. These depthreadings are correlated with time by thesynchronized watch at the surface.

The gyroscope rotor will tend to remain xed inspace. Friction about thetilt axis which isiminirnized by the use of ball bearings 64 and 66 will`produce a slight tendency for the gyroscope to precess in azimuth. Thedirectional effectof the gyroscope,however, is suciently great toovercome the small precessional force occasioned by slight frictionabout'the tilt axis 'so'that my gyroscope will indicate substantiallytrue `direction for alon'gperiod of time, much longer than bythe timeconsumed by lowering the instrument into a bore hole and removing ittherefrom.

Since the azimuth scale on flange 1 28 is fixed in a plane normal to theaxis of the bore hole, to-achieve correct indications in the passage ofthe instrument down the bore hole, I maintain thespin axis of thegyroscope in a plane normal to the axis of the instrument. Anyinclination'of the instrument 'will cause the contacting point carriedIby the arm 156 to contact one or the other of the segments 14S or 150.This contact will complete the circuit of the gyroscope servomotor toapply a torque around the azimuth axis in a direction to process thegyroscope aboutthe tilt axis until the spin axis is in a plane normal tothe axis of the instrument. VIt is to be noted that the axis of theinstrument coincideswith the axis of the borehole. Since most `boreholes-have inclinations which lie generally in a single vertical plane,thc direction indicated by the azimuth scale will be a true direction,and it will be unnecessary toapply a correction for angularity betweenthe azimuth scaleand the horizon as must be done when the spin axis ismaintained in a plane normal to true gravity, as disclosed in mycopending application, Serial No. 2,975. This correcting torque alsoovercomes the disturbing precessions due to friction in the gyroscoperotor bearings 40 and 42, which precessions tend to reducethedircctional effect of the gyroscope.

The gyroscope rotor will always maintain a fixed position with respectto space. As the earth rotates, the spatial direction and theterrestrial direction in azimuth will have a relative movement, which atthe equator amounts to l degrees an hour. That is, a point on theequator of the earth moves at'the rate of l5 degrees an hour so that thedirection from the rst point to the pole will malte an angle of 15degrees with the direction `tothe pole from that point one hour later.At intermediate points between the pole and the equator, this rate ofchange of direction with respect to space varies as a vfunction of thecosine of the latitude.

in order to enable my gyroscope to indicate a true terrestrialdirection, it is necessary to precess the gyroscope in azimuth in adirection to 'compensate for the rotation of the earth. The direction ofprecession must be from the elevated pole toward west, since the earthrotates on its axis from west toward east. fFor example, if the locationof the bore hole to be surveyed were 41 100 north, the rate at which thegyroscope must be processed in azimuth is ll1724" an hour. Such aprecession in azimuth is produced by a torque applied around the tiltaxis in a direction depending on the direction of spin. i accomplishthis by means of the weight 256 and the scale 258. Scale 258 iscalibrated so that when the weight is set to a value corresponding tothe cosine of the latitude of a place, the weight will cause a torqueabout the tilt axis which produces a precession about the azimuth axisin the correct direction at a rate which is represented .by 15 cos L perhour. Since I attach my weight-256 on only one side ofthe gyroscopehousing, it will be necessary to change the direction of rotation of`the gyroscope motor in south latitudes.

As the instrument is lowered into the bore hole, the Cardan ring 72will'remain inthe alignment to which it was originally set. The azimuthscale 128 is carried by the'Caidan ring sothatit will remain in a fixeddirection irrespective of axial rotation of the instrument duringlowering. When the instrument is inclined due to deviations V,from thevertical in the bore hole, the base 202 which carries the scales rotatesuntil the weight 232 occupies the lowgravityfposition. The roller 228and a plate 224 produce frictional damping tending to stabilize the basein its low gravity position without undue oscillation. The arrangementis such that the friction damping is proportional tothe angle ofinclination. The arrangement furthermore permits settling at low angles,since the friction in the upperbearing 192 is very small. The devices212, 214 and 216 mounted on the base 202 will indicate the inclinationand azimuth as is explained in detail in my copending application,Serial No. 2,975.

Where the bore hole is generally helical in shape, there will be agyratory motion of the instrument around a vertical axis. Since theCardan ring is insensitive to rotation about any axis at right angles tothe Cardan axis, an errorv will be introduced by this gyratory motion.Referring now to Figures 8 and 9, the line A lnclicates the direction oftrue gravity, and the line A indicates the axis of the bore hole B.Since the Cardan ring axis is located with respect to the gyroscopehousing and the instrument must align itself with the bore hole, theCardan axis will coincide with the axis A. Let w represent the angularvelocity around the axis of true gravity A and represent the anglebetween axis A and the direction of true gravity A. The angular velocityw which `tends to cause rotation about the axis A of true gravity may berepresented as a vector in the direction of the axis A. This vector maybe resolved into two components, w cos in the direction of the bore holeaxis and w sin at right angles to the bore hole axis. The component wsin tends to cause rotation about an axis at right angles to the Cardanaxis and will not induce any error in indicated direction since 'theCardan is insensitive to forces tending to cause rotation about axes atright angles'to the Cardan axis. The components w cos however, tends tocause rotation about the `Cardan axis and will therefore induce anerror. During any time t the angular displacement in the plane of thehorizonowing to the vector w may be represented as wt. At the same timethe angular displacement in the plane of the bore hole as a result ofthe vector w will be wt cos Let us assume that, in the absence of avelocity w, the reference direction selected lies along tilt axis. Let prepresent the angle between the tilt axis and the true referencedirection measured in the plane of the horizon in the presence of avelocity w. Let tp' represent the angle between the tilt axis and theindicated reference direction measured in a plane normal to the axis ofthe bore hole in the prescnceof a velocity w.

lf a measurement Yis made in the plane of the horizon in -the presenceof the velocity w, at any time l the angle p equals wt. If the samemeasurement is made in a plane making an angle with the horizontal planethe angle equals wt cos 6. From Ythe foregoing it wlll lreadily beappreciated that the relationship between fp and p may be expressed as:

direction referred to the plane of the horizon. I The difference Abetween the true direction of maximum tilt and the indicated directionof maximum tilt will be the same as the deviation between the referencedirection qa in the plane of the bore hole and the reference direction oin the horizontal plane. The difference in direction Agb, or the errorof the indicated direction from true direction at any given point in thebore hole may be represented by:

Where p1 is an angle at the point in the borehole where the measurementis started and p2 is an angle at the point in the bore hole at which themeasurement ends.

IIt will be seen that I have accomplished the objects of my invention. Ihave lprovided a self-contained apparatus for surveying bore holes inwhich the direction of the inclination of the bore hole is indicatedWi-th reference to an azimuth scale oriented by a gyroscope. I haveprovided the gyroscope with means for maintaining the spin axis in aplane normal to the axis of the bore hole so that for holes havinginclinations generally in a single vertical plane, the directionindications will be true and require no correction. This means alsomaintains the maximum directional efect of the gyroscope by correctingfor errors which would otherwise be introduced by processions resultingfrom friction in the gyroscope rotor bearings. In addition my gyroscopeis automatically corrected for errors due to procession caused by thecomponent of the rotation of the earth on its axis. My self-containedunit has means for indicating inclinations with respect to the verticaland a photographic unit for making a record of the amount and directionof the inclinations at predetermined times.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims. It is further obvious that various changes may be made indetails within the scope of the claims without departing from the spiritof the invention. It is therefore to be understood that this inventionis not to be limited to the specic details shown and described.

Having thus described my invention, what I claim is:

1. In an apparatus for surveying bore holes, an elongated casing adaptedto be lowered through the bore hole to take a position with itslongitudinal axis parallel to the axis of the bore hole adjacent thepositions of the casing as it moves through the bore hole, a gyroscopehaving a spin axis, a suspension for said gyroscope mounted in saidcasing and including a Cardan ring said suspension including meansmounting said Cardan ring in said casing for pivotal movement about anaxis extending in the direction of the longitudinal axis of said casing,said suspension including means mounting said gyroscope for pivotalmovement about a tilt axis perpendicular to said spin axis and to thepivotal axis of the Cardan ring, means for maintaining the spin axis ofsaid gyroscope in a plane normal to the longitudinal axis of saidcasing, said means comprising a pair of sectors symmetrically disposedwith respect to a plane passing through the longitudinal axis of thecasing, a contact point responsive to movement of the spin axis withrespect to said casing axis, a servomotor having a shaft, means forconnecting said servomotor shaft to said Cardan ring to apply a turningforce to said Cardan ring about its pivotal axis, said contact pointadapted to cornplete circuits to said servomotor through said sectors toenergize said servomotor to precess said gyroscope about the tilt axis.

2. Apparatus as in claim 1 including additional means for applying atorque about the tilt axis of said gyroscope as a function of the cosineof latitude whereby to process the gyroscope about its azimuth axis tocorrect 10 for errors in terrestrial direction which would otherwise beintroduced by the rotation of the earth on its axis.

3. Apparatus as in claim l including additional means for applying atorque about the tilt axis of said gyroscope as a function of the cosineof latitude whereby to precess the gyroscope about its azimuth axis tocorrect for errors in terrestrial direction which would otherwise beintroduced by the rotation of the earth on its axis, said last namedmeans comprising a weight, means for carrying said weight for movementtoward and away from the tilt axis of said gyroscope and means formoving said weight.

4. Apparatus as in claim l including a housing for said gyroscope, aguide member mounted on the housing and a lweight carried yby said guidemember for movement therealong, said weight providing means foradjusting the center of gravity of said gyroscope and housing to a pointwhere it coincides with the horizontal plane passing through the tiltaxis.

5. Apparatus for surveying bore holes comprising in combination anelongated casing adapted to be lowered through the bore hole to take aposition with its longitudinal axis parallel to the axis of the borehole adjacent to the position of the casing at all positions of saidcasing as it is being moved through the bore hole, a gyroscope having aspin axis, a suspension for said gyroscope mounted in said casingandpincluding a Cardan ring said isuspension including means mountingsaid Cardan ring for pivotal movement about an axis -extending in thedirection of the longitudinal axis of the casing, said suspenpensionincluding means mounting said gyroscope in said Cardan ring for pivotalmovement about a tilt axis perpendicular to said spin axis and to thepivotal axis of the ACardan ring, a servomotor having a shaft, meansconnecting said vservomotor shaft to the Cardan ring to apply a turningforce to said Cardan ring about its pivotal axis and contact meansresponsive to movement of the spin axis with respect to the longitudinalaxis of said casing to start said servomotor, said servomotor rotat- Ving the Cardan ring to maintain the spin axis normal to the bore holeaxis.

6. Apparatus for surveying bore holes as in claim 5 including a housingfor said gyroscope and wherein said contact means includes a pair ofconducting sectors fixed on said Cardan ring, a contact arm pivotallymounted on said Cardan ring and a parallel motion connection betweensaid contact arm and said gyroscope housing, said contact arm resting inits normal position between said sectors when the spin axis is normal tothe bore hole axis, said parallel motion connection moving said contactarm to contact one of said segments when the spin axis moves relative tothe bore hole axis.

7. Apparatus for surveying bore holes as in claim 5 including a housingfor said gyroscope and wherein said contact means includes a pair ofconducting sectorsrixed to said Cardan ring, a contact arm pivotallymounted on said Cardan ring and a parallel motion connection betweensaid contact arm andsad gyroscope housing, said servomotor including apair of oppositely Wound windings, said pair of sectors 'being connectedto respective windings.

8. Apparatus for surveying bore holes as in claim 5 including means forapplying a torque about the tilt axis of said gyroscope as a function ofthe cosine of the latitude of the bore hole location. t

References Cited in the tile of this patent UNITED STATES PATENTS1,311,768 Gray et al. July 29, 1919 1,959,141 Sperry May l5, 19342,220,055 Fischel et al Oct. 29, 1940 2,381,438 Curry Aug. 7, 19452,462,541 Norden Feb. 22, 1949 FOREIGN PATENTS 132,688 Sweden -..n-7---" Aug. 14, 19,51

